Lactose is the chemical name for milk sugar, which occurs naturally in dairy products. Unlike table sugar, lactose doesn't have a particularly sweet taste. Nevertheless, its chemistry in the body is quite similar to that of table sugar. Due to the process by which you digest lactose, some individuals are lactose intolerant.
Structure
The lactose molecule has the chemical formula C12H22O11, which is identical to that of sucrose, which is table sugar. Like sucrose, lactose is a disaccharide, meaning it's made up of two smaller sugar units, or monosaccharides, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry." Each monosaccharide is ring-shaped, and lactose therefore has a structure that resembles two rings, chemically bonded together. The specific monosaccharides in lactose are glucose and galactose.
Digestion and Absorption
When you consume lactose, you must digest it into its constituent monosaccharides before you can absorb it. You accomplish this via the digestive enzyme lactase, found in the small intestine. Once you've split lactose into its components -- glucose and galactose -- you absorb them into the bloodstream, explains Dr. Lauralee Sherwood in her book "Human Physiology." The cells can then take up glucose and galactose, and use them for energy.
Utilization
Lactose is a source of energy to the cells because it breaks into monosaccharides that cells can burn or convert into storage molecules. If you take in more lactose than you need at a given time, you can store the excess. Your liver and muscles make an energy storage molecule called glycogen from glucose and galactose. Alternately, you can convert the monosaccharides into triglycerides, or fat molecules, and store them in adipose tissue.
Lactose Intolerance
Some people don't produce lactase in sufficient quantities to digest dietary lactose. This results in lactose intolerance, which causes bloating, intestinal discomfort, and diarrhea. The discomfort is due to lactose passing undigested through your small intestine into the large intestine, where native bacteria break it down. In the process, they produce large quantities of gas, leading to intestinal bloating and cramping. You can help prevent symptoms by taking supplemental lactase when you consume dairy.
References
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
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